1. Field of the Invention
The present invention relates to an inkjet printing device using colored ink containing a pigment-based color material and an image quality improvement liquid, and to an inkjet printing device configured to control a sense of gloss provided by images.
2. Description of the Related Art
In inkjet printing in which an image is formed on a print medium by applying ink ejected from a print head to a print medium to form dots, there has been a strong demand to print high-quality images on various print media. Furthermore, in particular, photorealistic print has recently been demanded. Thus, glossy paper, which provides image quality and tones equivalent to those of silver halide photography, is widely available on the markets.
For glossy paper, there are various demands for a sense of gloss provided by printed images. One of the demands is to print images with even gloss all over the print medium. To meet this demand, for example, Japanese Patent Laid-Open No. 2002-307755 discloses means for reducing gloss unevenness on the surface of printed matter with an image printed thereon; the gloss unevenness is inherent in pigment ink. The gloss unevenness is a problem resulting from a difference in glossiness between a printed area in which an image is printed with pigment ink and a non-printed area in which no image is printed. In Japanese Patent Laid-Open No. 2002-307755, whether a pigment-based colored ink is ejected through nozzles in a print head (whether ejection of the pigment-based colored ink is ON or OFF) is detected for each pixel. Transparent ink is applied to OFF pixels (the image in the non-printed area) with the colored ink not applied thereto. This makes the glossiness of the non-printed area equivalent to that of the printed area printed with the colored ink, improving gloss evenness.
On the other hand, there has been another demand to utilize a difference in the sense of gloss to mix glossy areas and less glossy areas together in the same print medium, thus exerting a special effect. For example, in a glossy photographic image, a less glossy character image may be desired to be printed. Printed matter with such images printed thereon exerts such an ornamental effect as to make the characters appear to bulge from the printed matter at a particular viewing angle, and can thus be used for “ornamental printing” applications for catalogs and graphic arts. Means using a colorless and transparent image quality improvement liquid for controlling the gloss may be used to realize these applications as described in Japanese Patent No. 4,040,417. Japanese Patent No. 4,040,417 discloses a method of controlling the glossiness in which when the image quality improvement liquid is applied, the number of scans performed by a print head and culling data used for each scan are changed so as to allow the printed matter to provide plural levels of sense of gloss using a simple configuration.
To uniformize the gloss of an image printed using pigment ink, it is necessary to mix dots of the pigment-based colored ink with dots of the image quality improvement liquid on the print medium instead of forming the colored ink and the image quality improvement liquid into separate layers, depending on the formation density of dots of the colored ink per unit print area. This is because the mixture of the dots of the colored ink and the dots of the image quality improvement liquid increases the likelihood of providing the surface shape with recesses and protrusions, thus suppressing the excessively high glossiness of certain gradation portions to make the gloss even at all gradation levels. This phenomenon will be described in the DESCRIPTION OF THE EMBODIMENTS section in detail.
On the other hand, to allow the effect of ornamental printing to be exerted by applying, to the print medium, the colorless and transparent image quality improvement liquid for controlling the gloss, a layer of the image quality improvement liquid (image quality improvement liquid layer) needs to be formed on a layer of the colored ink (colored ink layer) formed on the print medium, as an upper layer. That is, in order to achieve the ornamental printing, the image quality improvement liquid needs to be formed as what is called an overcoat layer.
As described above, to improve the gloss evenness of an image printed using the pigment-based colored ink, the image quality improvement liquid needs to be applied to the print medium as required so that the dots of the colored ink are mixed with the dots of the image quality improvement liquid to roughen the surface shape, thus reducing the mirror surface glossiness. On the other hand, for ornamental printing, the image quality improvement liquid needs to be overcoated on the colored ink. Japanese Patent Laid-Open No. 2002-307755 and Japanese Patent No. 4,040,417 do not disclose any technique for meeting both the above-described requirements.
Two functions can be simultaneously provided by having, as a print head for applying the image quality improvement liquid, two types of print heads, a print head for ornamental printing (print head for overcoating) and a print head for improving the gloss evenness (print head for dot mixed printing). However, in this case, another problem occurs: mounting of two types of print heads may increase costs and the size of the printing device.